Is there a form that allows to sell shirts with different sizes and prices?

I am not sure which t-shirt order form to use I need one that provide size quantity and color. That will show a change in price for bigger sizes

You won't need a specific form for this, what you need is to know how to implement these on your form.

When you add a Payment Field, you'll have an option to add your own products. And each PRODUCT can have its own set of OPTIONS / QUANTITIES, where you can also set a SPECIAL PRICING respectively.

To aid you, I'm listing down some guides below on how to apply this on your form.

Related guides:

What-is-Special-Pricing

How-to-Add-Options-to-Payment-Forms 

In case you have a question, don't hesitate to ask.

I am still confused because I don't know which form to choose
...

No worries, I guess there's a confusion because you're looking for a readily available form instead of building/creating one.

I'm afraid you'd have to build the form on your own, from scratch. Although you may find some similar forms in our Templates Gallery, there's still no 100% chance that you'll get exactly what you're looking for.

Complete guide: How-to-use-the-form-templates 

Thus, the reason why I cited some guides that will aid you setting up a form, of your own, and based on your own requirement. This way, you get to decide how the form will be set up and will have total control over it.

If you need more help on how to get started, kindly refer to our guide on How-to-create-your-first-web-form